The present invention relates to a pattern formation method and a pattern formation material, and more particularly, it relates to a pattern formation method for forming a resist pattern, used for forming a semiconductor device or a semiconductor integrated circuit on a semiconductor substrate, by using exposing light of a wavelength not longer than a 180 nm band and a pattern formation material used in the pattern formation method.
Currently, in fabrication of a mass storage semiconductor integrated circuit, such as a 64 Mbit dynamic random access memory (DRAM) and a logic device or a system LSI with a 0.25 xcexcm through 0.15 xcexcm rule, a resist pattern is formed by using a chemically amplified resist material including a polyhydroxystyrene derivative and an acid generator as principal constituents with KrF excimer laser (of a wavelength of a 248 nm band) used as exposing light.
Moreover, for fabrication of a 256 Mbit DRAM, a 1 Gbit DRAM or a system LSI with a 0.15 xcexcm through 0.13 xcexcm rule, a pattern formation method using, as exposing light, ArF excimer laser lasing at a shorter wavelength (of a 193 nm band) than the KrF excimer laser is now under development.
The chemically amplified resist material including a polyhydroxystyrene derivative as a principal constituent has high absorbance against light of a wavelength of a 193 nm band because of an aromatic ring included therein. Therefore, exposing light of a wavelength of a 193 nm band cannot uniformly reach the bottom of a resist film, and hence, a pattern cannot be formed in a good shape. Accordingly, the chemically amplified resist material including a polyhydroxystyrene derivative as a principal constituent cannot be used when the ArF excimer laser is used as the exposing light.
Therefore, a chemically amplified resist material including, as a principal constituent, a polyacrylic acid derivative or a polycycloolefin derivative having no aromatic ring is used when the ArF excimer laser is used as the exposing light.
On the other hand, as exposing light for a pattern formation method capable of coping with high resolution, an electron beam (EB) and the like are being examined.
When the EB is used as the exposing light, however, the throughput is disadvantageously low, and hence, the EB is not suitable to mass production. Thus, the EB is not preferred as the exposing light.
Accordingly, in order to form a resist pattern finer than 0.10 xcexcm, it is necessary to use exposing light of a wavelength shorter than that of the ArF excimer laser, such as Xe2 laser (of a wavelength of a 172 nm band), F2 laser (of a wavelength of a 157 nm band), Kr2 laser (of a wavelength of a 146 nm band), ArKr laser (of a wavelength of 134 nm band), Ar2 laser (of a wavelength of a 126 nm band), soft X-rays (of a wavelength of a 13, 11 or 5 nm band) and hard X-rays (of a wavelength not longer than a 1 nm band). In other words, a resist pattern is required to be formed by using exposing light of a wavelength not longer than a 180 nm band.
Therefore, the present inventors have formed resist patterns by conducting pattern exposure using F2 laser (of a wavelength of a 157 nm band) on resist films formed from conventionally known chemically amplified resist materials respectively including a polyhydroxystyrene derivative represented by Chemical Formula A, a polyacrylic acid derivative represented by Chemical Formula B and a polycycloolefin derivative represented by Chemical Formula C. 
Now, a method for forming a resist pattern by using any of the aforementioned conventional chemically amplified resist materials and problems arising in the conventional method will be described with reference to FIGS. 2A through 2D.
First, as shown in FIG. 2A, the chemically amplified resist material is applied on a semiconductor substrate 1 by spin coating and the resultant is heated, so as to form a resist film 2 with a thickness of 0.3 xcexcm. Thereafter, as shown in FIG. 2B, the resist film 2 is irradiated with a F2 laser beam 4 through a mask 3 for pattern exposure. Thus, an acid is generated from the acid generator in an exposed portion 2a of the resist film 2 while no acid is generated in an unexposed portion 2b of the resist film 2.
Next, as shown in FIG. 2C, the semiconductor substrate 1 is heated with a hot plate 5 at, for example 100xc2x0 C. for 60 seconds.
Then, the resist film 2 is developed with an alkaline developer, thereby forming a resist pattern 6 as shown in FIG. 2D.
However, as shown in FIG. 2D, the resist pattern 6 cannot be formed in a good pattern shape, and there remains much scum on the semiconductor substrate 1. Such problems occur not only in using the F2 laser beam as the exposing light but also in using any of the other light of a wavelength not longer than a 180 nm band.
Accordingly, a resist pattern cannot be practically formed by irradiating a resist film formed from any of the aforementioned chemically amplified resist materials with light of a wavelength not longer than a 180 nm band.
In consideration of the aforementioned conventional problems, an object of the invention is forming a resist pattern in a good pattern shape by using exposing light of a wavelength not longer than a 180 nm band with minimally producing scum.
The present inventors have studied the cause of the conventional problems occurring in using the conventional chemically amplified resist materials and have found the following:
First, the chemically amplified resist materials have high absorbance against light of a wavelength not longer than a 180 nm band. For example, a resist film with a thickness of 100 nm formed from the chemically amplified resist material including a polyhydroxystyrene derivative has transmittance of 20% at most against a F2 laser beam (of a wavelength of a 157 nm band).
Therefore, various examination has been made on means for improving the transmittance of a chemically amplified resist material against light of a wavelength not longer than a 180 nm band. As a result, it has been found that a unit represented by Chemical Formula 1 below and a unit represented by Chemical Formula 2 below can improve the transmittance against light of a wavelength not longer than a 180 nm band.
The present invention was devised on the basis of the aforementioned finding, and specifically provides pattern formation materials and methods described below.
The first pattern formation material of this invention comprises a base polymer including a first unit represented by Chemical Formula 1 and a second unit represented by Chemical Formula 2; and an acid generator: 
wherein R1 and R2 are the same or different and selected from the group consisting of a hydrogen atom, a chlorine atom, a fluorine atom, an alkyl group and an alkyl group including a fluorine atom; R3 is a protecting group released by an acid; m is an integer of 0 through 5; and a and b satisfy 0 less than a less than 1,0 less than b less than 1 and 0 less than a+bxe2x89xa61.
Since the base polymer of the first pattern formation material includes the first and second units respectively represented by Chemical Formulas 1 and 2, the transmittance of a resist film against light of a wavelength not longer than a 180 nm band can be improved. Also, since R3 is released from the second unit owing to the function of an acid so as to generate hexafluoroisopropyl alcohol, the solubility in a developer of an exposed portion of the resist film can be improved. Therefore, the contrast in the solubility between the exposed portion and an unexposed portion of the resist film can be improved, and the wettability of the resist film is improved so as to improve adhesion between the resist film and a substrate. Furthermore, since the second unit has a benzene ring, resistance against dry etching can be improved.
In the first pattern formation material, the base polymer can be prepared through radical polymerization of the first unit and the second unit.
Alternatively, in the first pattern formation material, the base polymer can be prepared by obtaining a polymer through radical polymerization of the first unit and a precursor obtained before substituting R3 for the second unit and allowing R3 to bond to the precursor included in the polymer.
The second pattern formation material of this invention comprises a base polymer including a first unit represented by Chemical Formula 1, a second unit represented by Chemical Formula 2 and a third unit represented by Chemical Formula 3; and an acid generator: 
wherein R1, R2 and R4 are the same or different and selected from the group consisting of a hydrogen atom, a chlorine atom, a fluorine atom, an alkyl group and an alkyl group including a fluorine atom; R3 is a protecting group released by an acid; m and n are integers of 0 through 5; and a, b and c satisfy 0 less than a less than 1,0 less than b less than 1,0 less than c less than 1 and 0 less than a+b+cxe2x89xa61.
Since the base polymer of the second pattern formation material includes the first through third units respectively represented by Chemical Formulas 1 through 3, the transmittance of a resist film against light of a wavelength not longer than a 180 nm band can be largely improved. Also, R3 is released from the second unit owing to the function of an acid so as to generate hexafluoroisopropyl alcohol and the third unit has hexafluoroisopropyl alcohol. Therefore, the solubility in a developer of an exposed portion of the resist film can be improved so as to largely improve the contrast in solubility between the exposed portion and an unexposed portion of the resist film, and the wettability of the resist film can be improved so as to largely improve the adhesion between the resist film and a substrate. Furthermore, since the second unit and the third unit respectively have benzene rings, the resistance against dry etching can be largely improved.
In the second pattern formation material, the base polymer can be prepared through radical polymerization of the first unit, the second unit and the third unit.
Alternatively, in the second pattern formation material, the base polymer can be prepared by obtaining a polymer through radical polymerization of the first unit and the third unit and substituting R3 for some of H of OH groups of the third unit included in the polymer.
The third pattern formation material of this invention comprises a base polymer including a first unit represented by Chemical Formula 1 and a second unit represented by Chemical Formula 4; and an acid generator: 
wherein R1 is a hydrogen atom, a chlorine atom, a fluorine atom, an alkyl group or an alkyl group including a fluorine atom; R5 is a protecting group released by an acid; p is an integer of 0 through 5; and a and d satisfy 0 less than a less than 1,0 less than d less than 1 and 0 less than a+dxe2x89xa61.
Since the base polymer of the third pattern formation material includes the first and second units, the transmittance of a resist film against light of a wavelength not longer than a 180 nm band can be improved. In particular, since the second unit has a norbornene ring, the transmittance of the resist film against light of a wavelength not longer than a 180 nm band can be further improved than that attained by the first pattern formation material. Also, since R5 is released from the second unit owing to the function of an acid so as to generate hexafluoroisopropyl alcohol, the solubility in a developer of an exposed portion of the resist film can be improved. Therefore, the contrast in the solubility between the exposed portion and an unexposed portion of the resist film can be improved, and the wettability of the resist film can be improved so as to improve the adhesion between the resist film and a substrate. Furthermore, since the second unit has a norbornene ring, the resistance against dry etching can be improved.
In the third pattern formation material, the base polymer can be prepared through radical polymerization of the first unit and the second unit.
Alternatively, in the third pattern formation material, the base polymer can be prepared by obtaining a polymer through radical polymerization of the first unit and a precursor obtained before substituting R5 for the second unit and allowing R5 to bond to the precursor included in the polymer.
The fourth pattern formation material of this invention comprises a base polymer including a first unit represented by Chemical Formula 1, a second unit represented by Chemical Formula 4 and a third unit represented by Chemical Formula 5; and an acid generator: 
wherein R1 is a hydrogen atom, a chlorine atom, a fluorine atom, an alkyl group or an alkyl group including a fluorine atom; R5 is a protecting group released by an acid; p and q are integers of 0 through 5; and a, d and e satisfy 0 less than a less than 1,0 less than d less than 1,0 less than e less than 1 and 0 less than a+d+exe2x89xa61.
Since the base polymer of the fourth pattern formation material includes the first through third units, the transmittance of a resist film against light of a wavelength not longer than a 180 nm band can be largely improved. In particular, since the second unit and the third unit respectively have norbornene rings, the transmittance of the resist film against light of a wavelength not longer than a 180 nm band can be further improved than that attained by the second pattern formation material. Also, R5 is released from the second unit owing to the function of an acid so as to generate hexafluoroisopropyl alcohol and the third unit has hexafluoroisopropyl alcohol. Therefore, the solubility in a developer of an exposed portion of the resist film can be improved so as to largely improve the contrast in the solubility between the exposed portion and an unexposed portion of the resist film, and the wettability of the resist film can be improved so as to largely improve the adhesion between the resist film and a substrate. Furthermore, since the second unit and the third unit respectively have norbornene rings, the resistance against dry etching can be largely improved.
The first pattern formation method of this invention comprises the steps of forming a resist film by applying the first pattern formation material on a substrate; irradiating the resist film with exposing light of a wavelength not longer than a 180 nm band for pattern exposure; and forming a resist pattern by developing the resist film after the pattern exposure.
Since the first pattern formation material is used in the first pattern formation method, the transmittance of the resist film against light of a wavelength not longer than a 180 nm band can be improved, the contrast in the solubility between an exposed portion and an unexposed portion of the resist film can be improved, the adhesion between the resist film and the substrate can be improved, and the resistance against dry etching can be improved.
The second pattern formation method of this invention comprises the steps of forming a resist film by applying the second pattern formation material on a substrate; irradiating the resist film with exposing light of a wavelength not longer than a 180 nm band for pattern exposure; and forming a resist pattern by developing the resist film after the pattern exposure.
Since the second pattern formation material is used in the second pattern formation method, the transmittance of the resist film against light of a wavelength not longer than a 180 nm band can be largely improved, the contrast in the solubility between an exposed portion and an unexposed portion of the resist film can be largely improved, the adhesion between the resist film and the substrate can be largely improved, and the resistance against dry etching can be largely improved.
The third pattern formation method of this invention comprises the steps of forming a resist film by applying the third pattern formation material on a substrate; irradiating the resist film with exposing light of a wavelength not longer than a 180 nm band for pattern exposure; and forming a resist pattern by developing the resist film after the pattern exposure.
Since the third pattern formation material is used in the third pattern formation method, the transmittance of the resist film against light of a wavelength not longer than a 180 nm band can be further improved, the contrast in the solubility between an exposed portion and an unexposed portion of the resist film can be improved, the adhesion between the resist film and the substrate can be improved, and the resistance against dry etching can be improved.
The fourth pattern formation method of this invention comprises the steps of forming a resist film by applying the fourth pattern formation material on a substrate; irradiating the resist film with exposing light of a wavelength not longer than a 180 nm band for pattern exposure; and forming a resist pattern by developing the resist film after the pattern exposure.
Since the fourth pattern formation material is used in the fourth pattern formation method, the transmittance of the resist film against light of a wavelength not longer than a 180 nm band can be further largely improved, the contrast in the solubility between an exposed portion and an unexposed portion of the resist film can be largely improved, the adhesion between the resist film and the substrate can be largely improved, and the resistance against dry etching can be largely improved.
In any of the first through fourth pattern formation methods, the exposing light may be light of a wavelength of a 110 through 180 nm band, such as a Xe2 laser beam, a F2 laser beam, a Kr2 laser beam, an ArKr laser beam or an Ar2 laser beam, a soft X-ray beam of a wavelength of a 1 through 30 nm band, or a hard X-ray beam of a wavelength not longer than a 1 nm band.